Clinical features
- Rare
- Young adolescents
- Aggressive clinical course
Cytopathology (similar to Ewing Family tumours (EFT) elsewhere)
Classical:
- Tigroid background
- Small round blue cells
- Dark and light cells
- Isolated cells and rosettes
- Nuclei with fine chromatin
- Scarce cytoplasm with small glycogen vacuoles
Immunocytochemistry
- CD99: positive
- NSE: positive
- Chromogranin: generally negative
- Synaptophysin: positive- focal
- Cytokeratin: focal positivity-( seen in only 10-20% of the tumour)
Genetic studies:
- t(11;22)(q24;q12)
Differential diagnosis
- Neuroblastoma
- Generally in the adrenal gland; can involve the upper pole of the kidney
- Typically in younger children
- Fibrillary background
- CD99: negative
- Absence of t(11;22)(q24;q12)
- Nephroblastoma-blastemal type
- Younger patients
- Blastemal cells are more aggregated than the PNET cells
- CD99: can be positive
- Absence of t(11;22)(q24;q12)
- WT1:positive
- Clear cell sarcoma of the kidney
- Younger patients
- Nuclei with clear chromatin
- CD99: negative
- Absence of t(11;22)(q24;q12)
Main points
Molecular demonstration of t(11;22)(q24;q12) is sometimes essential, to distinguish from Wilms’ tumour